Development of coral banks in the Porcupine Seabight: Do they have Mediterranean ancestors?

This paper presents an overview of the geological, biological and oceanographical environment of coral banks in the Porcupine Seabight. The study area is characterised by well delimited geographic clusters of coral banks, each characterized by their typical bank morphology and environmental setting. In the central part two mound provinces are recognised: complex flat topped seafloor mounds in the 'Hovland mound province', and a large number of smaller N-S elongated buried mounds in the 'Magellan mound province'. Along the eastern margin of the basin partly buried and outcropping mounds form the 'Belgica mound province'. The banks are mound-shaped elevations, hosting living deepwater coral (Lophelia sp., Madrepora sp., Desmophyllum sp., Dendrophylla sp.) and associated fauna. This biological active layer covers a dead assemblage of corals clogged with mud. Endogenic and exogenic environmental parameters are evaluated in time and related to the geomorphological response of the banks. All coral banks, buried or outcropping, occur in association with current-induced features (e.g., scouring features, dunes) and steep palaeo and present seabed slopes. Only a few banks are outcropping in the present setting which suggests that environmental conditions were more favourable for bank development in the past. The depth range of these outcropping mounds coincides with the top of the dense Mediterranean OutflowWater, where current enhancement may control the coral distribution not only nowadays but also in the initial phase of coral bank development. The distribution of corals in the southeastern North Atlantic and the actual link with Mediterranean water suggest a possible migration of corals within the Mediterranean water into the Atlantic. The startup phase of coral bank development in Porcupine Seabight was simultaneous for all provinces, after a Late Pliocene period of erosion and non-deposition. Sediment stress time variations, largely controlled by currents, play an important role in bank development. Coral banks accrete by active baffling of sediment by the biological framework and extension of the biological cap (catch-up phase). Once this fragile system between sedimentation and biological growth is out of balance, the framework will progressively be clogged with sediment (keep-up phase). Once sediment dominates the structure the coral banks get buried and draped by sediment (give-up phase).